JPS636592A - Display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] In a display device that displays characters by scanning a display screen using raster scanning, the reading time of character codes from a code buffer and the conversion from character codes to character patterns in a character generation circuit are disclosed. To increase the number of dots constituting a character pattern without changing the scanning speed or the raster scanning completion time for one screen, display clear characters, and prevent flickering on the display screen.

[Industrial application field]

The present invention relates to a device that performs display by scanning a display screen using raster scanning, and particularly to a display device that displays clear characters by increasing the number of dots in a character pattern.

With the development of the information society, various display devices have come to be used in information processing devices. Among these display devices, those using a cathode ray tube (CRT) are most commonly used.

By the way, in recent years, the display screen of CRT display devices has become larger,
In addition, there is a growing demand for displaying clear characters and precise figures, but in order to satisfy this demand, it is necessary to increase the number of display dots on the display screen.

Generally, a CRT display device displays a display screen by raster scanning, and as the number of display dots increases, the number of scanning lines also increases, so it takes longer to complete raster scanning for one screen.

If the time required to complete the raster scan for one screen becomes longer, the display screen will flicker, but an economical means to prevent this is desired.

[Conventional technology]

FIG. 4 is a block diagram showing an example of a conventional display device.

The microprocessor 1 reads and operates a program stored in the memory 3, processes data input from the keyboard 2, creates a character code, and stores this character code in the code buffer 4 of the memory 3.

The character codes stored in the code buffer 4 are sequentially read out, converted into a display dot pattern by the character generation circuit 5, and displayed on the display screen of the CRT 6.

[Problem that the invention seeks to solve]

If the number of display dots is increased to display clear characters using the conventional method, as described above, the time required to complete raster scanning for one screen becomes longer, and screen flickering called flicker occurs. That is, since the display time per dot becomes longer, the dots that emit light for the first time gradually become darker.

This is because the raster scanning time for one screen cannot be shortened because the time required to read the character code from the code buffer 4 and the time for the character generation circuit 5 to convert the character code into a display dot pattern is limited. .

In order to shorten the reading time of character codes, it is necessary to increase the number of codes read at once from the code buffer 4, and to speed up the time to convert character codes into display dot patterns (in order to speed up the time to convert character codes into display dot patterns, a character generation circuit with short access time is required). However, there is a problem in that the character generating circuit 5, which has a short access time, is very expensive.

[Means for solving problems]

FIG. 1 is a block diagram of the principle of the present invention.

In Figure 1, a control circuit 7 and a bitmap memory 8 are added to Figure 4, and the time to read character codes from the code buffer 4 and the speed of conversion to display dot patterns in the character generation circuit 5 remain the same as before. It is something.

The control circuit 7 controls the code buffer 4 to read the character code at the same speed as before and send it to the character generation circuit 5, and writes the display pattern converted by the character generation circuit 5 to the bitmap memory 8. The display dot pattern read out at a reading speed faster than the writing speed is sent to the CRT 6 and displayed.

[Effect]

With the above configuration, the bitmap memo I78 can send the display dot pattern to the CRT 6 at a faster speed than before under the control of the control circuit 7, so the time required to complete raster scanning for one screen can be shortened. This makes it possible to display clear characters with a large number of dots, without flickering on the screen.

〔Example〕

FIG. 2 is a block diagram of a circuit showing an embodiment of the present invention.
FIG. 3 is a time chart explaining the operation of FIG. 2.

The control circuit 7 sends the write address to the RAM 9 of the bitmap memory 8, and writes the display dot pattern sent from the character generation circuit 5 in units of, for example, 16 bits at the rising edge of the write pulse shown in FIG.

The control circuit 7 also sends a transfer address to the RAM 9, and sends a transfer timing synchronized with the display timing synchronized with the horizontal synchronization signal shown in FIG. If the display dot pattern is to display, for example, 64 characters consisting of 32x32 dots in the - column, 32x64 bits are transferred to the shift register 10 at one time.

From terminal A, a display clock generated based on the horizontal synchronizing signal is supplied to the shift register 10 as a read pulse and to the RAM 9 as a write pulse.

The display door pattern for one column transferred to the shift register 10 is sent 32 bits at a time to the CRT 6 for display at the rising edge of the read pulse shown in FIG.

In this case, the write pulse is synchronized with the display timing,
- 64 pulses are sent out per raster scanning light, and 64 pulses are sent out similarly for the readout pulse.

A display dot pattern is written into the RAM 9 independently regardless of the read cycle, and the display dot pattern is written to the CRT from the shift register 10 at twice the writing speed.
6 is sent out.

Therefore, characters composed of 32x32 dots can be displayed using the same code buffer 4 and character generation circuit 5 used to display characters composed of 16x16 dots.

〔Effect of the invention〕

As explained above, the present invention does not require the use of an expensive character generation circuit with a fast access time, and uses a code buffer with the same reading speed as the conventional one, and can produce clean characters with a large number of character dots without flickering. It can be displayed.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is a block diagram of a circuit showing an embodiment of the present invention, Fig. 3 is a time chart explaining the operation of Fig. 2, and Fig. 4 is a block diagram of the principle of the present invention.
The figure is a block diagram showing an example of a conventional display device. In the figure, 1 is a microprocessor, 2 is a keyboard, 3 is a memory, 4 is a code buffer, 5 is a character generation circuit, and 6 is a CRT. 7 is a control circuit, 8 is a bitmap memory, 9 is a RAM, and 10 is a shift register.

Claims (1)

[Scope of Claims] A code buffer (4) that stores character codes, etc., and a character generation circuit (5) that converts the character codes stored in the code buffer (4) into character patterns. In a display device that displays characters, etc. by scanning, a bitmap memory (8) that stores the character pattern sent out by the character generation circuit (5), reading the character pattern from the bitmap memory (8), A control circuit (7) for controlling reading of character codes from the code buffer (4) is provided, and the number of bits written from the character generation circuit (5) to the bitmap memory (8) in synchronization with the display clock is provided. A display device characterized in that the number of bits read from the bitmap memory (8) in synchronization with the display clock is increased.